Cannabinoids are molecules that are detected by cannabinoid receptors in humans and other animals. Endocannabinoids are produced within the human body and function to stimulate the human endocannabinoid system. Phytocannabinoids are produced by plants. There are at least 120 cannabinoids that have been identified. Many of these cannabinoids share the chemical formula C21H30O2. There are various plant sources for phytocannabinoids, including plants from the genus Cannabis L. Hemp is a common term for a variety of Cannabis Sativa L. species. Hemp is rich in cannabinoids and its extracts are used as medicine.
Other common agricultural crops such as flax are known to produce cannabinoids such as cannabidiol (CBD). CBD is a well known cannabinoid that is used for a variety of purposes including to manage pain and seizures without adverse effects on the user.
Echinacea is a medicinal herb that has been found to contain cannabimimetic N-Alkyamides. N-acylethanoamines are a class of fatty acid compounds which are known to have a significant impact on biological signaling. One of these is anandamide, which is a cannabinoid of interest in many studies.
At least one species of rhododendron has been shown to contain the cannabinoid cannabichromene (CBC). New Zealand liverwort may contain perrottetinenic acid, which is considered to be a cannabinoid very similar in function to trans-Δ9-tetrahydrocannabinol (THC). The interaction between perrottetinenic acid and the human CB1 receptor and associated health benefits are currently being studied. The breeding and engineering of plants to yield increased levels of perrottetinenic acid is under development.
In some regions of the world, the soils and water are contaminated with naturally occurring and man-made compounds and elements that are toxic to humans. These contaminants include residual pesticides, agricultural fertilizers, naturally occurring microbiological metabolites, and other compounds including toxic minerals and metals.
In recognition of the potential for soil contamination, the State of Washington, in the United States has promulgated maximum concentrations of metals that commercial fertilizers can contain. These are regulated by Washington Administrative Code (WAC) Title 16, Chapter 200. The concentration of these metals allowed in fertilizers sold are shown in Table A below.
TABLE AWashington Standards For Metals in FertilizersMetalsLbs./acre/yr.Arsenic (As).297Cadmium (Cd).079Cobalt (Co).594Mercury (Hg).019Molybdenum (Mo).079Nickel (Ni).713Lead (Pb)1.981Selenium (Se).055Zinc (Zn)7.329
These metals are considered contaminants when found in nutraceutical and food products. While the need for fertilizers is well documented, it is also documented that many plants uptake some of these metals in greater abundance than necessary. Normally, this leads to a balance between agricultural needs and safety. Unfortunately, these contaminant standards were not devised considering that agricultural herbs would play such a prominent role in modern pharmacopeia.
In the United States herbal medicine has become a multi-billion dollar industry. One of the leading herbal medicines is cannabis, in its various forms. While there is much focus on Marijuana as a medicine, the Hemp plant is expected to surpass marijuana production as an agricultural and medicinal crop.
Most patients that use of marijuana and hemp for medicinal purposes prefer not to smoke the flower directly, but instead prefer orally consuming a concentrated oil, or edible products made from such oil. A market segment also prefers vaporizing oil as a safer alternative to smoking. The problem is that concentrating herbal and botanical remedies into essential oils also concentrates contaminants, including metals.
There are other sources of contamination of agricultural products, including botanical herbs. Where the plant is not properly cultivated and harvested, mold and other microbial pathogenic organisms may grow on the plant. Microbes may not be harmful by themselves, but they may produce metabolites that function to inhibit competing microbes. The may be produced when the plant grows and after it is harvested.
Aflatoxins, ochratoxins, trichothecenes, zearalenone, fumonisins, deoxynivalenol tremorgenic toxins, ergot alkaloids, and other alkaloids can be toxic to not only to competing microbes, but also to humans, particularly when concentrated. Aflatoxins, particularly Aflatoxin B1, can cause health problems at elevated levels and have been well studied to document levels that are deemed safe.
When botanical extracts including cannabis extracts are made, the contaminants in the plant material may be concentrated in the final product.
The American Herbal Products Association (AHPA 2013) has proposed maximum limit for aflatoxin in dried, unprocessed herb products:                Total aflatoxins should be no greater than 20 parts per billion        Aflatoxin B1 should be no greater than 5 parts per billion        